Some helminthsAn intestinal worm which grows large enough to be seen with the naked eye when mature but which is microscopic when administered in helminthic therapy. [https://en.wikipedia.org/wiki/Helminths Wikipedia:Helminths] cause cancer, while others protect against it

In spite of having parasitesAn organism that lives in or on another organism (its host) and benefits at the host’s expense. (The organisms used in helminthic therapy are, strictly speaking, not parasites, but mutualists, because they have a mutually beneficial symbiotic relationship with their hosts.) that are classified as inducers and promoters of some neoplasms, others are reported as negative regulators of cancer.” [1]

Emerging evidence indicates that certain parasitesAn organism that lives in or on another organism (its host) and benefits at the host’s expense. (The organisms used in helminthic therapy are, strictly speaking, not parasites, but mutualists, because they have a mutually beneficial symbiotic relationship with their hosts.)… are causative agents of malignancies such as bladder cancer caused bv schistosomes and cholangiocarcinoma by liver flukes… On the contrary, some parasiteAn organism that lives in or on another organism (its host) and benefits at the host’s expense. (The organisms used in helminthic therapy are, strictly speaking, not parasites, but mutualists, because they have a mutually beneficial symbiotic relationship with their hosts.) infections or molecules seem to display protective effects on some cancers, such as is the case with Echinococcus. [2]

HelminthsAn intestinal worm which grows large enough to be seen with the naked eye when mature but which is microscopic when administered in helminthic therapy. [https://en.wikipedia.org/wiki/Helminths Wikipedia:Helminths] that have been identified as being carcinogenic include the fish-borne trematodes Opisthorchis viverrini and Clonorchis sinensis and the blood fluke Schistosoma haematobium, all of which are categorised by the International Agency for Research on Cancer as Group 1 biological carcinogens. [3][4]

The helminthsAn intestinal worm which grows large enough to be seen with the naked eye when mature but which is microscopic when administered in helminthic therapy. [https://en.wikipedia.org/wiki/Helminths Wikipedia:Helminths] used for therapeutic purposes (NAthe human hookworm, Necator americanus, TTthe human whipworm, Trichuris trichiura, TSthe porcine (pig) whipworm, Trichuris suis and HDHymenolepis diminuta, a murine (rat) tapeworm.) are not carcinogenic (see Helminthic therapy safety), but one helminthic therapist has suggested that, since some solid mass tumours like to surround themselves with regulatory immune cells, it may be unwise to increase this cell population in patients with a history of solid mass tumours. [5]

The protective role of helminthsAn intestinal worm which grows large enough to be seen with the naked eye when mature but which is microscopic when administered in helminthic therapy. [https://en.wikipedia.org/wiki/Helminths Wikipedia:Helminths]

HelminthsAn intestinal worm which grows large enough to be seen with the naked eye when mature but which is microscopic when administered in helminthic therapy. [https://en.wikipedia.org/wiki/Helminths Wikipedia:Helminths] may be able to elicit anti-tumor immune responses that can lead to protection from tumorigenesis, or even to cancer regression.

Cancer has been linked to inflammation, which is controlled by helminthsAn intestinal worm which grows large enough to be seen with the naked eye when mature but which is microscopic when administered in helminthic therapy. [https://en.wikipedia.org/wiki/Helminths Wikipedia:Helminths]

HelminthsAn intestinal worm which grows large enough to be seen with the naked eye when mature but which is microscopic when administered in helminthic therapy. [https://en.wikipedia.org/wiki/Helminths Wikipedia:Helminths] and their products may potentially treat cancer

HelminthsAn intestinal worm which grows large enough to be seen with the naked eye when mature but which is microscopic when administered in helminthic therapy. [https://en.wikipedia.org/wiki/Helminths Wikipedia:Helminths] exert antitumor effects via several mechanisms of action.

The beneficial effects reported for some parasiticAn organism that lives in or on another organism (its host) and benefits at the host’s expense. (The organisms used in helminthic therapy are, strictly speaking, not parasites, but mutualists, because they have a mutually beneficial symbiotic relationship with their hosts.) diseases on tumorigenesis range from the induction of apoptosis, activation of the immune response, avoiding metastasis and angiogenesis, inhibition of proliferative signals, to the regulation of inflammatory responses that promote cancer. [6]

Worm-derived molecules could be potential candidates for anti-cancer drugs.

Infection with other microorganisms may also help to reduce cancer risk

Researchers found that enhanced biodiversity (of bacteria and worms) was associated with better immune responsiveness. Specifically, they found better responses to vaccination, better T-cell responses, and much higher levels of "natural" antibodies, which have been shown to be important in fighting cancer. [7]

BCG vaccination in infancy confers a survival advantage for melanoma patients, and vaccination of adults against yellow fever may have a similar effect.

Infection with the feline parasiteAn organism that lives in or on another organism (its host) and benefits at the host’s expense. (The organisms used in helminthic therapy are, strictly speaking, not parasites, but mutualists, because they have a mutually beneficial symbiotic relationship with their hosts.), Toxoplasma gondii, stimulates the body to produce natural killer cells and cytotoxic T cells, which wage war on cancer cells.

Rather than the presence of infectious microorganisms increasing cancer risk, a lack of them may be the greater problem.

…attenuated responses to tumor antigens as a result of biome depletion might underlie, at least in part, the proposed connection between increased rates of cancer and biome depletion. Further, decreased levels of “natural” IgG and IgM observed in biome depleted (laboratory) environments could exacerbate the problem, since the natural antibody repertoire is involved in tumor surveillance. In this manner, decreased tumor surveillance in biome depleted environments could promote cancer progression and operate synergistically with biome depletion-associated inflammation, a potential initiator and promoter of carcinogenesis. [8]

When a helminthAn intestinal worm which grows large enough to be seen with the naked eye when mature but which is microscopic when administered in helminthic therapy. [https://en.wikipedia.org/wiki/Helminths Wikipedia:Helminths], itself, gets cancer

This rare case in which a man died after a tapewormA helminth with a flat, ribbon-like, segmented body. Only the murine (rat) tapeworm, Hymenolepis diminuta, is used in helminthic therapy and this generally does not reach adulthood in humans so requires regular dosing of HDC. inside him developed cancer, involved a helminth that is not used in therapy.